7 DATs, 2 SCS cards

Doug Ledford dledford at dialnet.net
Thu Feb 19 09:31:37 PST 1998


Derek Seaman wrote:
> 
> I am going to be constructing a system with 7 HP C1599A 4mm DAT drives, 2
> 2940U SCSI cards, and 1 Seagate ST34572 HD and 1 Plextor 12/20x CD-ROM. The
> DATs will all be on one card and the HD & CD-ROM will be on the other SCSI
> card.
> 
> This system will be used to make tape copies which will be released to the
> U.S. Navy Fleet, so system stability is an absolute must.
> 
> Does anyone see a problem with the above setup? The 7 DATs will be in an
> external case using Granite Digial Teflon SCSI cables and terminators. I
> spared no expense with cables and terminators.

I don't forsee a problem, but you'll want to check the tape write speed vs.
the tape SCSI bus negotiation speed on those 7 tapes.  For example, if they
will all write to tape at a rate of 1.25MB/s, and they negotiate on the bus
at 10MB/s, then the bus will be very close to saturated when writing to all
7 tape devices (7 x 1.25 = 8.75MB/s total combined write speed, and with all
tapes at 10MB/s, you'll be close to the bus speed limit, plus when you add
in the overhead of command processing and what not, you could actually reach
a point where you can't keep all tape drives going at once at maximum
speed).
 
> Which Kernel/SCSI rev. is the most stable in terms of SCSI drivers? This
> system has to be rock solid. All 7 DAT will be used at once so the SCSI bus
> will be QUITE busy.

I've been testing my latest driver with tape drives pretty extensively,
doing things like 5 and 6 GB backups just to see if it works properly (using
the Arkeia backup software) and they've been going off without a hitch.
 
> Any comments would be greatly appreciated. The system will be running Red
> Hat 5.0.

RedHat's standard 5.0 kernel shipped with a 2.0.32 kernel with my Nov05
patch already applied (I found this out when people started emailing me when
they had a problem, because it had a message at boot up that gave my email
address for the aic7xxx driver in that kernel :).  There is a bug in that
patch that does effect tape drives and CD-ROMs most notably, so you will
probably want to upgrade the kernel immediately.

-- 

 Doug Ledford  <dledford at dialnet.net>
  Opinions expressed are my own, but
     they should be everybody's.

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